Overweight and obese individuals are at increased risk for coronary heart disease (CHD). Losing weight by means of dietary restriction greatly reduces vascular disease risk. The most common dietary restriction protocol implemented is daily calorie restriction (CR). Another dietary restriction regimen employed, although far less commonly, is alternate day modified fasting (ADMF). ADMF involves a feed day where food is consumed ad-libitum, alternated with a fast day, where food intake is partially reduced. Results from our 12- week pilot study show that adherence to ADMF exceeds that of CR after 8 weeks of treatment. This increased adherence to ADMF results in greater weight loss, which produces more pronounced improvements in CHD risk. What has yet to be determined is whether adherence to ADMF remains near maximal for longer treatment durations (24 weeks), and if this improved adherence results in greater reductions in body weight and CHD risk, versus CR. Once weight loss is achieved, weight maintenance is extremely important as CHD risk can increase if weight is regained. Whether ADMF is an effective strategy for weight maintenance remains unknown. Accordingly, the aims of this proposal are: Aim 1: To establish that adherence to ADMF is greater than that of CR during a 24-week intervention period and to determine if increased adherence to ADMF results in greater weight loss; Aim 2: To establish that greater reductions in body weight by ADMF over a 24-week period will result in greater improvements in traditional CHD risk parameters (blood pressure, plasma lipid levels, cholesterol synthesis rate, LDL particle size, and CRP) and emerging CHD risk parameters (fat cell- derived hormones, body fat distribution, and fat cell size) in comparison to CR; and Aim 3: To establish that ADMF is an effective diet therapy to maintain weight loss and sustain improvements in CHD risk indicators, and to compare changes in cognitive and behavioral components of eating between ADMF and CR subjects. A 52-week randomized, controlled, parallel-arm feeding trial will be implemented to test these objectives. The trial will be divided into 3 consecutive intervention periods: (1) 4-week baseline; (2) 24-week weight loss with food provided; and (3) 24-week weight maintenance with no food provided. Overweight and obese subjects (n = 90) will be randomized to 1 of 3 groups: (1) ADMF, 75% energy restriction on the fast day and ad libitum fed on the feed day; (2) CR, 25% restriction everyday; or 3) control, 100% energy intake every day. During the weight maintenance phase, ADMF subjects will consume 25% of their energy needs on the fast day and 175% of their needs on the feed day, while CR and control subjects will consume 100% of their needs every day. Our findings will show that ADMF can be implemented as an alternative to CR to help overweight and obese individuals lose weight, maintain weight loss, and sustain reductions in CHD risk. This study will also generate insights into the specific behavioral changes that occur with ADMF that explain why ADMF is a successful diet strategy for weight maintenance.